The present invention generally relates to a rotary piston internal combustion engine and, more particularly, to an engine housing structure for the rotary piston internal combustion engine.
To minimize the emission of noxious unburned components of an exhaust gas from a rotary piston internal combustion engine to the atmosphere, the recent trend has been to employ an exhaust gas purifying device, such as a thermal reactor, in the exhaust system of the rotary piston internal combustion engine. As is well known to those skilled in the art, combustion of the unburned components of the exhaust gas within the thermal reactor is brought about by the effect of the elevated temperature of the exhaust gas emerging from the rotary piston internal combustion engine. Therefore, the higher the temperature of the exhaust gas introduced into the thermal reactor, the more effective the combustion of the unburned exhaust gas components brought about within the thermal reactor.
In view of the operating characteristic of the thermal reactor currently used, various attempts have heretofore been made to avoid any excessive reduction of the temperature of the exhaust gas to be eventually introduced into the thermal reactor, which may result in ineffective combustion or a failure to reburn the unburned exhaust gas components within the thermal reactor. One of these attempts is to minimize, or substantially eliminate, the heat transfer to the forcibly cooled engine housing from the exhaust gas, by insulating the exhaust passage formed in the engine housing, such as by the use of a tubular insert inserted into the exhaust passage with an adiabatic space formed around said tubular insert, or by the use of a sleeve of heat insulating material pressure-fitted into the exhaust passage.
The above described conventional technique is satisfactory insofar as the temperature of the exhaust gas flowing through the exhaust passage within the engine housing is concerned. However, considering the whole process of flow of the exhaust gas, the mere provision of the tubular insert or sleeve in the exhaust passage is insufficient in the sense that the conventional technique does not satisfactorily avoid any reduction of the temperature of the exhaust gas which occurs prior to the exhaust gas entering the exhaust passage. As is well known to those skilled in the art, in a rotary piston internal combustion engine, the contact area between the exhaust gas in one of the variable-volume working chambers and the interior wall surface of the engine housing facing said one of the working chambers is so large that the temperature of the exhaust gas at the time of its generation may readily be lowered at the time the exhaust gas is ready to enter the exhaust passage since the engine housing is forcibly cooled by a fluid coolant which may be either air or liquid.
Moreover, the thermal reactor currently used is such that satisfactory and effective combustion of the unburned exhaust gas components, if the temperature of the exhaust gas is sufficiently high, takes place with a relatively small amount of the unburned components introduced thereinto, but will require a relatively large amount of the unburned components if the temperature of the exhaust gas is relatively low. Because of and in consideration of this operating characteristic of the thermal reactor, in order to avoid a possible failure to reburn, or otherwise carry out an ineffective combustion of, the unburned exhaust gas components within the thermal reactor due to the reduced temperature of the exhaust gas, a relatively enriched air-fuel mixture has heretofore been supplied into the engine. This has been considered one of the major causes of the high consumption of fuel in the rotary piston internal combustion engine the exhaust system of which includes such a thermal reactor. Since combustion of the unburned exhaust gas components within the thermal reactor may be said to be initiated by a process of `self-ignition` relying, not solely, but mostly, on the elevated temperature of the exhaust gas, reduction in temperature of the exhaust gas, inter alia, adversely affects on the amount of fuel consumed by the rotary piston internal combustion engine.